1. Field of the Invention
The invention relates to a device for exchanging objects, in particular writing instruments, between two holders embodied substantially alike and open at one side. To effect the transfer of an object by means of the approach of their open sides oriented toward one another, these holders are movable relative to one another in a plane which extends substantially at right angles to their longitudinal axes.
2. Brief Description of the Prior Art
In a known device of this kind (described in German published application, DE-OS No. 29 13 690), a change of writing instruments is to be accomplished in a computer-controlled drawing system. A writing instrument is held in the holder of the drawing head by two leaf springs, disposed opposite one another, with ends lightly gripping the writing instrument and pressing it against a stationary inner face, located opposite the opening in the holder, of the receiving area. The free ends of the leaf springs protrude somewhat in the direction of the transfer of the writing instrument to the holder of the instrument magazine, and the holder in the instrument magazine has two correspondingly embodied springs.
If the writing instrument is held in the holder of that drawing head and the drawing head approaches the instrument magazine, then in this state the free ends of the springs of the holder provided in the instrument magazine are located closer together, because of the absence of one writing instrument, than the free ends of the springs of the holder in the drawing head, which are spread apart by the writing instrument inserted between them. As a result, the free ends of the springs of the instrument magazine come into contact with the outer circumference of the writing instrument, and upon the further approach of the drawing head toward the instrument magazine these free ends are spread apart. As a consequence, they touch the protruding free ends of the springs of the holder in the drawing head and push their way in between these springs and the writing instrument, until they come to engage the writing instrument and thereby withdraw it from the holder of the drawing head upon the reversal of the movement of the drawing head.
When a writing instrument is inserted from the instrument magazine into the drawing head, the springs of the holders function in the same manner as described above, but in this case the springs of the holder of the drawing head push their way in between the springs of the holder of the instrument magazine and the writing instrument.
Although this known device for exchanging writing instruments functions relatively simply and reliably, it has the disadvantage that the position of the writing instrument in the holder of the drawing head is not defined precisely, because it is substantially determined by the characteristics of the two springs, which can vary with use. As a result, it may happen that when exchanging one writing instrument producing a particular line width for another which produces a line of different width, for instance, and attempting with the new instrument to continue a line drawn by the old instrument, the new line having the different width will not be centered precisely with respect to the line segment drawn previously.